Numerical investigation of the effects of flow rate and water temperature on membrane performance in anaerobic membrane reactors

Anaerobic membrane bioreactors (anMBR) are the applications that used in wastewater treatment. These reactors consist of a fully mix anaerobic reactor where biological treatment occurs and an ultrafiltration (UF) membrane. These porous membranes are in the form of plates or pipes and act as water filtering instrument. One of the important difficulties in anMBR application is the insufficient amount of water passing through the membrane; so that is the decrement in water flow rate. The decreased flow rate may cause the process interruption and results in poor treatment quality. In the present study, the effect of flow velocities on the water flux and on the solute deposits in the flat-plate membrane was numerically investigated. For this purpose, an open source CFD analysis program, the OpenFOAM software, was used. The analysis utilized the approach known as forward osmosis (FO), which relies on the repulsive force caused by the chemical potential between the feed and draw sides of the membrane. Effect of mean inlet velocities both for equal and different feed and draw side velocity values on the membrane performance were presented in terms of velocity distribution, water flux, and solute deposits on the membrane. In addition, for the case of thermal equilibrium between feed and drive side, effect of temperature on water flux was examined. Numerical fındings indicate that the mean inlet velocities are the effective parameters for the membrane performance. It was observed that the proportional relationship between the increasing mean inlet velocity and the water flux changed significantly after the mean velocity of 0.1 m/s. After this mean velocity, the ratio of water flux to mean velocity decreased approximately 10 times compared to before.As the inlet velocities precribed in diiferent manner it was observed that high draw inlet velocity causes to increase the water flux.Finally, it was observed that the treatment performance decreased with temperature due to the change in physical properties, and it was concluded that 35 0C, which is still valid in practice, is the most appropriate treatment temperature.